Project 2

Title= Project 2 -SOC % and Heat measuring by using Simulink Tool.

Contents of the project:-

1)Aim of the project

2) Heat generation and SOC estimation techniques explaination

3)Simulink model

4)Summery

5)Conclusion.

Aim of the project: -

The Main Aim is to determine the (a) The maximum heat generation of the battery and (b) SOC of the battery at 2 *104second of the battery operation by using given data with help of MATLAB /SIMULINK tools.

Heat generation and SOC estimation technique explanations: -

Heat Generation: -

If cells or batteries get too hot, they can rupture or explode the Lithium and Lithium-ion cells/batteries can catch on fire when they rupture, creating even more of a safety hazard.

To ensure safe operation over the entire intended operating range of a cell or battery, it is crucial that the battery engineer understands the fundamentals of internal heat generation and be able to calculate the expected adiabatic temperature rise of a cell or battery under any operating condition.

Heat generation Sources: -

The following sources are basically caused heat inside the battery pack.

- Cell temperature

- Ambient Temperature

- State of charge

- C-rate percentage

- Internal Resistance

- Number of Cycles used

- Cell Electrochemistry.

Types of heat: -

Basically, in battery component the heat will be classified into Two types

1) Joule Heat:-

When a current is flowing through a resistance, there is heat dissipated in the resistor. This heat dissipation is called joule heating. Joule heating is also known as ohmic heating.

This is determined by using the Ohm's law as follows:-

From ohm’s Law,

V = IR --------------(1)

where,

V= Voltage

I = Current

R= Resistance

Power: -

power (P) = V *I

where,

V= Voltage

I = Current

but we know that V = I * R

Then,

Power P = I²* R-----------------------(2)

where,

P= power

I = Current

R= Resistance

Now,

Joule heat = Power * time

we know that, power (P) = I² * R

then

Joule heat = Power * time

Joule heat H = I² * R * t--------------------------------(3)

Where,

H = Joule Heat

I = Current

R = Resistance

t = Time

2)Entropic Heat:-

This Entropic heat is defined as The rate of change of "OCV" (Open Circuit Voltage) with respect to Temperature.

It is measured in mV/K.

It is a function of temperature and state of charge (SOC).

The increase in Entopic heat of a system(dS): -

dS = δQ / δT

where,

δQ = heat transfer

δT = The absolute temperature.

Therefore,

Total Heat generated by battery = Joule Heat +Entopic Heat

Estimation of SoC: -

State of Charge:-

It is the real-time or actual capacity of the battery compared to its full capacity.

It is measured in terms of percentage (%).

Let us consider If battery 100% SoC means the battery is fully charged to its capacity, and 0% SoC means it’s fully discharged.

State of charge (SOC) is the level of charge of an electric battery relative to its capacity.

The units of 'SOC' are percentage points (0% = empty; 100% = full).

SOC= 20 % SOC= 40 % SOC = 100 %

The SoC is estimated basically using following 3 Methods: -

1)Voltage Translation Method:-

This Voltage Translation method is determine the SOC by using the battery "Open Circuit Voltage (OCV)".

Voltage translation method is the least accurate method to do so, because as the lithium-ion charge-discharge voltage cycle shows, the voltage is largely flat for a large region of the cycle; therefore, it does not give an accurate SOC.

The voltage translation method is generally used in applications like consumer electronics (battery banks,trimmer,torch lights) and also in small capacity energy storage systems.

Formula: -

Voltage Translation Method: -

SoC % = Soc % Full / Number of parameters used for determination of SoC

Errors in voltage translation method-

- Voltage fluctuation

the voltage fluctuation is due to the varying speed on the road,which leads to varying torque requirement by the motor.furthermore, T is directly proportional to current.

- Noise in the system

- cell chemistry

for different cell chemistries the OCV vs SOC curves are different.

Pros of voltage translation method-

-it is easy to implement

-it is cheaper compared to other methods

Cons of voltage translation method-

- it has high error in reading

- it is not effective for electric vehicle application.

2)Coulomb Counting Method: -

The Coulomb counting method counts the charge of the battery through current sensing, measuring how much current is flowing into the battery and how much current is flowing out of the battery.

Current is continuously monitored. Most all low-cost electronic products use the Coulomb counting method, as it is less expensive than the other more precise methods.

Formula: -

SOC Formulae: -

1)SOC %= (Total charge input / Max.battery capacity.)*100

2)

where,

Cn- battery nominal capacity in Ah

Z(t) - State of charge in %

i(t) - instantaneous cell current

t - time

ni - coulomb efficiency

Zo - Initial state of charge in %

pros of Coulomb Counting Method

- It has high accuracy

Cons of Coulomb Counting Method

-it increase in error rate with respect to time,temperature and life cycle.

3) Combination of voltage translation and coulomb counting

By Combination of voltage translation and coulomb counting, the error rate increment with respect to time and life cycle in coulomb counting method is calibrated with voltage translation.

Pros of this method

- it has higher accuracy.

Cons of Combination of voltage translation and coulomb counting method.

- the error rate will the same as CC method if the calibration is done periodically.

a) Maximum Heat generated by the Battery

Given data: -

From the formulae: -

Heat generated by battery pack = Joule heat + Entropy heat

Where,

Joule heat = I² R t

Entropy factor = 2

Entropy heat = 2 (I² R t)

therefore,

Heat generated by battery pack = I² R t+ 2(I² R t) ------ (A)

from the given data,

Maximum current = -0.896 A

Resistance = 0.5 mΩ = 0.0005 Ω

time = 120sec

From eqn (A)

Joule Heat generated by battery pack = (I² R t)

= (-0.896) ² * (0.5) * 120

=48.168 mJ--- (B)

Entropy heat generated by battery pack = 2 (I² R t)

= 2*48.168

= 96.336 mJ----(C)

From A, B and C, we get

Heat generated by battery pack = I² R t+ 2(I² R t)

= 48.168 mJ + 96.336 mJ

= 144.504 mJ

Therefore,

Maximum Heat generated by battery pack =144.504 milli joules.

b)The SOC of the battery at 2 *104second of the battery operation

Simulink model: -

For creating the Simulink model, we are using the following blocks: -

1. Signal Builder: - To Give the Signal to as input to the other blocks.
2. Controlled current source: -Converts the Simulink input signal into an equivalent current source. The generated current is driven by the input signal of the block.
3. Battery: - Implements a generic battery model for most popular battery types. Temperature and aging (due to cycling) effects can be specified for Lithium-Ion battery type.
4. Bus selector: -This block accepts a bus as input which can be created from a Bus Creator, Bus Selector or a block that defines its output using a bus object.
5. Series RLC branch: -Implements a series branch of RLC elements. Use the 'Branch type' parameter to add or remove elements from the branch.
6. Powergui: -Set simulation type, simulation parameters, and preferences.
7. scope: -To plot the output signals in graphical view

Procedure :-

• for this model firstly ,we have to add the Excel file for signal builder block by using the below steps

- For adding the excel file double click on the signal builder block.

- Then a new window will open as follows

- Now click on the File open

- After select the import file from option.

- After another window will open as follows.

- from this window browse the required excel file.

- then another window will open after extract the file as follows.

- Now check mark the name of our excel sheet and select the option below as replace the existing data sheet.

-after click on the confirm selection.

- after that click on the apply button.

- after complete this process we get the window as follows.

- After completing this process.

- this signal builder output is given to the controlled current source block.

- from this current controlled source block and battery both are connected in series and in between a resistance is added by using series RLC branch block.

Battery parameter block:-

Series RLC branch ,select only R branch with following parameters.

- after SOC will be getting the scope by using the bus selector block by selecting the signal as SOC%.

- After this SOC will plotted by using the scope block.

Result Scope-

- From the above graph we consist of two parameters graphical view.

Top Plot (Signal Builder Plot)

- from this graph we can says that the given drive cycle is consist of a negative current in always and this value is mostly from - 1.0304 Amps to -0.896 Amps.

- Maximum current is -0.896 Amps.

Bottom plot (SOC%)

- from this graph we can conclude that the SOC % is always 100% because the vehicle in regenrative breaking mode in this mode the battery gets charged always due to this reason the SOC% is always 100%.

Summery-

learning objectives: -

1) the outcomes from this project are Knowing about Heat generation finding in battery pack and Also about SOC measuring methodologies for the battery pack.

2) we can learn from this project that the Vehicle is in regenerative mode then the current as in negative direction hence the Battery gets charged and SOC is 100 %.

Conclusion-

1) Maximum Heat generated by battery pack =144.504 milli joules.

2)The SOC of the battery operation is 100% (Simulink model is also created and attached) and also the requirement files are uploaded.